One of the reasons rail trails are fairly popular is because it preserves the railroad right-of-way for potential future use. Even if the rails are removed and pavement put down, it's far cheaper to pull the pavement up and re-lay rails if you need the line in future (like for light-rail or commuter service) rather than to have to re-acquire the right of way again or build an entirely new line. The term is "railbanking." [0]

[0] https://en.wikipedia.org/wiki/Railbanking

This actually can become a problem in the future. Here in Montgomery County, Maryland there was an old rail line converted to a bike path but always with the intention of adding light rail to a portion of it.

20 years later, they started the project and the local cycling groups are upset because their path has to be split and rerouted in places to support the new line. Delayed the thing many years as a result.